A typical fluid delivery system includes a pumping device which pumps fluid from a reservoir under pressure to a system for use. An example of such a system is a fuel delivery system for an internal combustion engine, wherein fuel stored in a fuel tank is pumped to a fuel system for delivery to operate the engine. In a conventional fuel system for a spark ignition engine, the expected system operating pressure is 300 kPa to 400 kPa for fuel flow levels ranging from about 0 grams/second to in excess of 40 grams/second. When the fuel delivery system is a demand fuel system, i.e. wherein there is unidirectional fuel flow to the fuel system with no return line, volumetric flow to the fuel system may be managed by varying output of the fuel pump to the fuel system.
Under normal operation of the demand fuel system described above, the valve opens to permit flow of pressurized fluid from the pump to meet demands of the fuel system. Under a situation wherein engine operation changes and reduces demand for pressurized fuel, the fuel pump may reduce or discontinue volumetric flow. Such situations include extended deceleration of the engine, or deceleration of the vehicle employing the engine. Under this situation, there continues to be a need to maintain fuel pressure control in the fuel system. Under situations wherein the fuel system of the engine is exposed to elevated temperature while the engine is turned off, pressure in the system may become elevated. Elevated pressure in the fuel system may lead to an inability to precisely control fuel delivery during a subsequent engine starting event, which may affect emissions and startability.
There is a need to be able to control fluid pressure in a system under a range of pump and system operating conditions. There is a further need to be able to control fluid pressure in a system when the pump is not operating. There is a further need to prevent leakage from the system to the pump, or other areas. When the pump and system is a fuel system for an engine, there is a need to provide motive force for a venturi pump.